code: def test_str_accessor_cat_none():
      s = pd.Series(["a", "a", "b", "b", "c", np.nan], name="foo")
      ds = dd.from_pandas(s, npartitions=2)
  
      assert_eq(ds.str.cat(), s.str.cat())
      assert_eq(ds.str.cat(na_rep="-"), s.str.cat(na_rep="-"))
      assert_eq(
          ds.str.cat(sep="_", na_rep="-"),
          s.str.cat(sep="_", na_rep="-"),
      )
  
imports: from __future__ import annotations
  import contextlib
  import numpy
  import pytest
  import dask.dataframe
  from dask.dataframe._compat import PANDAS_GE_140, PANDAS_GE_210
  from dask.dataframe._pyarrow import to_pyarrow_string
  from dask.dataframe.utils import assert_eq, pyarrow_strings_enabled
label_desc: Use image node_id 13 for calling a global function with example usage: test_str_accessor_cat_none() without return types